Compound(s) mutagenic to bacteria have been isolated from feces of apparently healthy humans. Since most known carcinogens are mutagenic, it is possible that these mutagens are involved in the etiology of colon cancer. We have found that the mutagenicity of feces of certain donors can be greatly increased by anaerobic incubation and that this increase can be attributed to anaerobic bacteria. Using the technique of anaerobic incubation, it has been possible to produce enough of the mutagen to purify it. The chemical structure of this mutagen will be determined and the bacterial species responsible for the production of mutagen will be isolated and identified. We also plan to test the mutagen for mutagenic and/or carcinogenic activity in mammalian systems.